Carbon-free alloy



Patented Sept. 24, 1940 PATENT- OFFICE CARBON-FREE ALLOY Robert H.Canfield and Herman F. Kaiser, Washington, D. 0., Roy A. Gezelius,Somerville, N. J., and Henry S. Jerabek, Minneapolis, Minn.

No Drawing.

Application October 6, 1938, Serial No. 233,594

2 Claims.- (Cl. 75 170) (Granted under the act of March 5, 1883, asamended April 30, 1928; 370 0. G. 757)- This invention relates tocarbon-free alloys and to methods of heat treating and preparing themfor various uses:

It is an object of this invention to provide hard 5 alloys which aresubstantially free from carbon and which owe their hardness to thepresence of other metals. v

It is a further object of this invention to provide alloys which can besoftened and subsequently in hardened to the range of hardness oftool-steels without deformation or cracking.

It is a further object of this invention to provide alloys which possessthe red-hardness of stellite and the 18-4-1 tool steels while at thesame time possessing enough ductility and toughness to allow bendingwithout breaking.

It is a still further object of our invention to provide methods of heattreating and preparing these alloys which will allow working of them in20 a softened state and subsequent development of the quality ofhardness to the extent desired. Further objects of this invention willbecome apparent from a reading of the following description:

.25 In the art of tool making, as at present practiced, the metal of thetool derives its hardness mainly from the presence of carbon inthe formof metallic carbides. In simple steel it is cementite or iron carbidewhich -supplies the hardness; but in other steels it may be, inaddition, the carbides of chromium, tungsten, molybdenum or othermetals. In the case of metals which are not strictly steels, such asstellite and carbolloy, there are nevertheless carbides of f chromium,tungsten or other metals present, and it is to these substances that thealloys largely owe their hardness.

We have discovered that it is possible to make alloys of iron and cobaltwhich are substantially free from carbon, and owe their hardness to thepresence of small amounts of another metal or metals. Furthermore, themethod of developing this hardness is quite different from that usedwith steel, since our metal is softened by being quenched from a hightemperature, and subsequently hardened by an annealing treatment at atemperature somewhat lower than the one from which it was quenched. As aresult of the nature of this process it is possible to make articles ofintricate shape using ordinary machine-shop methods and later hardenthem uniformly without internal strain, without deformation or crackingand without exposing them to destructive atmospheres. Also, tools madeout of our metal may be used for cutting at temperatures nearly up tothat at which they have received their hardening anneal, without losingtheir usefulness as cutting tools at this elevated temperature. Thusthis alloy shares the property of red-hardness with such materials asstellite and the 18-4-1 5 tool steels. Our alloy, even in the hardenedcondition possesses considerable toughness and ductility, so that it isstill possible to bend it without. breaking it.

Our alloy can be prepared within a certain. 10 range of compositions andstill possess its distinctive qualities; but its typical analysisconsists of a base alloy of cobalt and iron 35% to which may be addedseveral other elements to a total amount of generally less than 5%. How-I ever, we have made useful alloys where the base composition variedbetween 62% cobalt, 38%.iron, and 68% cobalt, 32% iron, with additionsup to over six percent of other elements. The added elements (to thepresence of which the alloy owes 20 its distinctive hardeningproperties) are manganese and one or both of the elements chromium andmolybdenum. The presence of manganese is not essential to the alloy andit may be omitted, if desired. The manganese is. added in amounts 25 upto 1.5%, the chromium up to 3%, the molybdenum up to 5%; but all theseelements cannot be present at the same time in their maximum amountswithout entirely altering the nature of the alloy. This is illustratedin the 30 following table:

Total composition-Rockwell C -hardness Alloy No. 00 Fe Mn Cr M05 Max.Min.

It will be seen that while alloys 1 and'3, containing 2.3% chromium and5.4 molybdenum respectively, are both highly hardenable, alloy 5containing 2.2% chromium and 4.0% molybdenum, is even in its hardestcondition inferior to the others in their softest condition; it is infact an entirely difierent alloy metallographically. As for carbon, wehave. found that its efiect is detrimental; it does not enhance thehardness of the alloys'in their hardest state, while it tends to makethem too hard in their softest state. We keep it below 0.05%.

As already mentioned, these alloys can be in the original formofcastings, forgings; or rolled sections. The first step in preparingthe metal for further work is to quench it from a high temperature. Thistemperature varies according to the composition but is always above 1650F.

We preferably quench the metal in water or brine since even air-coolingmay be slow enough to permit some of the changes which producehardening. After this quenching operation the article will'be softenough (usually Rockwell -39) to permit any kind of machining operation,including milling, turning, drilling, cold-rolling and others. Ifnecessary to re-soften the metal, it can be quenched again. When thearticle is finally ready for hardening, we preferably pack it with steelwool in an annealing box, but any kind of suitable container can beused, and heat it in a furnace to a temperature and for a timedependent'somewhat on the composition and on the ultimate propertiesdesired; but generally the temperature-is above 800 F. and it is alwaysbelow 1200 FL; and the time is between one and twenty hours. Forexample, we took a piece of the alloy listed as No. 1 in the foregoingtable, and forged it into a bar square. We then quenched it in brinefrom 2000 F. After it had been sawed and milled to the form of a lathetool at Rockwell 0-39, we packed it in steel wool in a closed iron pipeand heated it to 1000 R; we kept it there for one hour and then removedit from the furnace. On cooling and unpacking, the

tool had a hardnesspf Rockwell (1-63 and was used in heavy turning of,machinery steel on a lathe, the out being so deep and fast that thecondition our alloy No. 1 already described afterbeing'magnetized'possessed a residual induction of 9000'8auss and acoercive force of 65 oersteds, and yet was soft enough to machine, andcould be cold bent or rolled without aifecting its magnetic properties.It was now heated to 1150 F. and cooled again, having remainedpermanently magnetized during the whole operation and re tainingafterwards a large proportion of its orginal residual induction.

Although we have mentioned only tools and permanent magnets asapplications of our alloy, there are other applications which willsuggest themselves to one versed in metallurgy and physics, and weinclude all'such applications in our specification. I

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment -of any royalties thereon or therefor.

- Having thus set forth and disclosed the nature of this invention, whatis claimed is:

1. An age hardenable alloy consisting of 58 to 68% cobalt, 28 to 38%iron and .4 to 3.0% chromium, with less than .05% carbon.

2. An age'hardenable alloy consisting of 58 to 68% cobalt, 28 to 38%iron and 1.0 to 6% molybdenum, with less than .05% carbon.

ROBERT H. CANFIELD. HERMAN F. KAISER. ROY A. GEZELIUS. I'ENRY S.JERABFK.

